Popcorn is a commonly consumed snack food produced by heating kernels of corn until the moisture within the kernel vaporizes into steam causing the starch within the kernel to temporarily gelatinize and the shell of the kernel to erupt. The internal moisture of the kernel is quickly heated to a temperature of approximately 356° F. (180° C.) to vaporize the moisture and pop the kernel. If the kernel is not sufficiently heated or is heated too slowly, the kernel will not pop. Similarly, if one side of the kernel is heated too quickly, the kernel shell can be damaged while the starch on the cold side has yet to gelatinize leading to less explosive popping, which in turn reduces popped volume and leads to chewier popcorn. A corresponding concern is that once the kernel is popped, the “foam” produced from the gelatinizing and re-hardening starch is easily burned giving the popcorn an undesirable taste and texture. A variety of methods are commonly employed to quickly heat popcorn kernels to the appropriate temperature while minimizing burning include: applying microwave energy to the kernels, cooking the kernels in hot oil or fat, baking the kernels with heat conducted through a heating surface, or blowing hot air across the kernels. The different methods can be incorporated into single use packaging for producing a single batch of popcorn, wherein the packaging is discarded after the popcorn is popped, or popcorn makers that can produce repeated batches of popcorn.
The most common popcorn makers cook the kernels in hot oil, fat or a combination thereof heated on a heating surface or pan supplying the necessary heat to pop the kernels. The cooking method efficiently heats the kernels to the appropriate temperature by conducting heat through the oil or fat directly to the kernels. The oil or fat can provide an additional benefit by imparting a desirable buttery taste or other flavor to the popped popcorn. A common alternative to the oil or fat cooking method for popping popcorn is baking the kernels with heat conducted through a heating surface without an oil or fat solution. However, a drawback of both the cooking and baking method is that the methods often waste substantial amounts of heat that is dissipated into the atmosphere. In both methods, the kernels are also typically placed on a heating surface disposed above a heat source. The heat source dissipates a large quantity of heat, some of which is transferred to the heating surface. The heating surface then conducts the heat to the kernels either through direct contact under the baking method or via an oil or fat solution under the cooking method. However, as a substantial amount of the heat output from the heat source is dissipated to the environment, popcorn poppers using either the cooking or baking method may function acceptably even though the heat source design is highly inefficient. Similarly, because the heat source simply radiates heat outwardly, different thermal zones may be formed on the heating surface each having different temperature responses depending on the distance and angle of incidence of the zone from the heat source. The uneven heating may cause some kernels to be under heated, locally over heated, or heat too slowly leading to substandard popping. Depending on the popper design, a fat or oil cooking solution may help evenly distribute the heat and/or control rate of heating resulting in improved popping; however, if a thick coating of oil or fat is required to yield improved popping performance, the monetary and health benefits of such a product may be compromised.
As the baked method of heating kernels does not cook the kernels in oil or fat, a topping is often applied during popping or after the popcorn is popped to impart a buttery taste or any other desirable flavor to the popcorn. Typically, a cover having an integrated topping reservoir is placed over the heating surface containing the kernels or popped popcorn. The topping reservoir can be arranged at the top of the cover and typically comprises vents in the cover such that the topping can be slowly drained through the vents in the cover onto the popcorn as the kernels are popped or after the popcorn is popped. Certain toppings, such as butter, are slowly melted by the steam released from the popped kernels such that the melting topping is slowly applied to the popcorn. Covers also commonly comprise air vents for venting the steam in close proximity to the reservoir or use the same vents for applying the topping to the popcorn to vent the steam. However, the air vents or shared vents often become fouled by the topping as the topping is drained into the cover causing a buildup in steam within the cover. Since the moisture cannot escape, the popcorn does not dry out enough and ends up tasting soggy or chewy.
The different methods of heating often include a mechanical stirrer or agitator to constantly mix the kernels during cooking insuring that the un-popped kernels are evenly heated and the popped kernels are not burnt. However, mechanical stirrers often cause the kernels to bunch or pile up rather than evenly distributing the kernels across the heating surface. The kernels within the bunches or piles are often either unheated or heated at different rates than evenly distributed kernels. Different heating rates can cause some kernels heated at faster rates to pop earlier than kernels heated at slower rates, which may result in the faster popping kernels being burned while the slower popping kernels remain un-popped. The bunches or piles of kernels often form in “blind spots” in the rotational path of the stirrer where the arm of the stirrer cannot reach the kernels or the kernels fall beneath the stirrer arm. A corresponding concern is that stirrers without blind spots may cause the kernels to bunch up against the stirrer arm and be pushed around the heating surface in a bunch rather than being evenly distributed over the heating surface. Even distribution of the kernels over the heating surface allows the kernels to absorb the heat more efficiently, which reduces popping time and reduces heat lost to the environment during the cooking period.